Margarine and shortenings prepared from vegetable oils are perceived by many as more healthy than butter and lard. This perception is justified because animal fats typically contain cholesterol and have higher levels of palmitic acid than common margarine oils. To date, however, it has not been possible to realize the full promise of the health benefits of margarine and related fatty products.
Some dietary fats present in butter and useful in making quality margarine, notably those high in lauric acid (12:0), myristic acid (14:0), or palmitic acid (16:0), have been reported to increase plasma cholesterol concentrations, while fats high in stearic acid do not (Bonanome, A., and Grundy, S. M., New Eng. Jour. Med. 318: 1244-1248 (1988)). In most diets, palmitic acid dominates this group of saturated fats (Keys, A., et al., Metabolism 14: 766-786 (1965)), so a decrease in dietary palmitic acid would be beneficial.
The plastic properties of margarine fats are improved through hydrogenation, but the resulting fats have been criticized as less healthy than vegetable oils with high cis unsaturation. Most natural vegetable fats and oils contain only cis double bonds, but partial hydrogenation results in the formation of trans fatty acid substituents. Recent studies have investigated the effect of trans fatty acids on raising low-density lipoprotein serum cholesterol levels and lowering high density lipo-protein serum cholesterol levels in adults fed fats having these acids (Mensink, R. P., and Katan, M. B., New Eng. Jour. Med. 323: 439-445 (1990)).
Margarines formulated with oils containing low levels of palmitic acid, e.g., safflower oil, canola oil, and sunflower oil, have been suggested, but these have a tendency to become grainy during storage because the polymorphism of the fat crystals tend to stable beta forms that have a coarse, sandy texture (Chrysam, M., in Bailey's Industrial Oil and Fat Products, vol. 3, Wiley-Interscience, 1985, pages 62 to 63). In severe cases, the crystal transformation may result in exudation of the liquid oil from the product and partial coalescence of the aqueous phase, which increases the microbiological susceptibility (ibid.). Randomization of the hard component (U.S. Pat. No. 4,316,919 to Pelloso and Kogan) or interesterification of the hard with part of the liquid portion (U.S. Pat. No. 4,230,737 to Heider and Wieske) have also been suggested to prevent texture problems, but these products have a partially hydrogenated component and contain trans fatty acids.
Various research efforts have been directed to the development of edible fats that mimic the physical and organoleptic properties of partially-hydrogenated fats but have diminished or zero trans acid contents. For example, interesterified fat products have been prepared using fully-hydrogenated hardstocks (U.S. Pat. No. 3,617,308 to Graffelman), including those having no trans isomers (List, G. R., et al., J. Amer. Oil Chem. Soc. 54: 408-413 (1977)). Fat blends using a stearin fraction instead of hydrogenated and interesterified fats have been disclosed for producing margarines (U.S. Pat. No. 4,366,181 to Dijkshoorn, et al.). Low trans fat products have also been prepared by fractionating an interesterified mixture of liquid and completely hydrogenated oil (U.S. Pat. No. 4,425,371 to Stratmann, et al.). However, these products are formulated with palmitic acid.
Another approach to low trans products makes use of directed interesterification to prepare fats from liquid oil without the aid of hydrogenation. For example, directed interesterification of sunflower and safflower oils at low temperatures in an aprotic solvent (U.S. Pat. No. 3,859,447 to Sreenivasan) or of corn oil with temperature cycling in the absence of solvent (U.S. Pat. No. 4,419,291 to Lathauwer, et al.) has been disclosed. However, using most oils, the technique yields a plastic product having limited functionality.
It would be desirable to have margarines and solid shortenings that are low in palmitic acid, have low levels of or no trans fatty acids, and have good functional and organoleptic properties.